Several techniques are known for delaying an analog signal, such as an audio frequency signal found in sound reproduction systems. A number of these techniques operate by converting the analog signal to a digital form which is then passed through a digital memory to be retrieved later and reconverted to analog form with a specified delay. A specific example of such a delay technique employs an analog-to-digital conversion based upon the delta-sigma modulation technique wherein the analog signal is converted to a sequence of binary ones and zeroes that are in turn applied to a shift register at a predetermined clock rate. The length of the shift register is a function of the desired delay interval and the clock rate required for a desired frequency response; the length increasing with both delay and frequency response desired.
Shift registers of a length sufficient to produce a delay useful in the audio field, for example, a significant fraction of a second, are an important cost item in the overall delay system. Where a specific delay interval is required, the only trade-off in shift register length comes at a sacrifice in frequency response which can in turn lead to a degradation in quality of the analog signal emerging from the delay system.